1. Field of the Invention
This invention relates broadly to continuous metal casting. More particularly, this invention relates to a method and apparatus for determining heat removal from a continuous caster during caster cooling operations. The invention may be used in connection with caster mold heat removal, as described below, as well as with spray cooling and roll cooling zones throughout the caster.
2. Description of the Prior Art
Continuous casting machines are used in the basic metals industry to continuously produce semifinished billets, slabs and the like from molten metal in a one-step solidification process. Generally, molten metal from a tundish is continuously introduced into a water-cooled mold where initial solidification takes place in the form of a frozen metal skin surrounding a liquid core as the cast product continuously leaves the mold. Complete solidification of the cast product occurs in spray cooling, roll cooling and radiation cooling zones beyond the caster mold.
In order to have successful caster operation, a precise amount of initial solidification or skin growth must continuously occur in the caster mold in relation to caster speed. If too much heat is removed from the mold, surface cracks and internal defects may develop in the strand. If too little heat is removed from the mold, a breakout of molten metal will occur in the caster which may result in serious consequences to both personnel and facilities. A key parameter for successful caster operation is knowledge of heat removal in the water-cooled mold. For any mold face of known properties the heat removal rate Q is proportional to the variables of cooling water flow rate W and the cooling water inlet to outlet temperature rise .DELTA.T in degrees F., and the constants K and Cp which pertain to coolant density and specific heat. Current practice used by most caster operators is to simply gauge mold heat removal by the value of cooling water temperature rise .DELTA.T.
The current practice of using mold .DELTA.T gauging approach has several deficiencies. For example, assume that during a steady state operation the heat removal rate Q is constant, then .DELTA.T will be inversely proportional to the water flow rate W. Therefore, changes in water flow rate W, which occur in actual practice, would change the .DELTA.T, thereby indicating a possible heat removal problem which in fact would not exist.
Another deficiency is attributed to the fact that many casters have adjustable molds which are designed with differing amounts of cooling water flow rates per unit length of mold face. For example, a 10 inches mold narrow face may have twice as much flow as a 10 inches section of a mold wide face. Assuming the same heat fluxes on these two mold faces, the .DELTA.T on the narrow face would be half the .DELTA.T on the wide face. Thus, using .DELTA.T as a guide to heat removal in this situation makes comparison between types of mold faces difficult.
In still another situation which deals with adjustable width and thickness caster molds, both the size of the face plates and the cooling water flow rate W are fixed for a given mold. However, when the width or thickness of the cast product is selected from a plurality of mold sizes in one adjustable mold and the cooling water flow rate W is constant, both the heat removal rate Q and the .DELTA.T will vary with cast product width and/or thickness. Thus, using .DELTA.T as a measure of heat removal rate again becomes very difficult because any standardized operating practice using .DELTA.T must then include variations for a plurality of different cast product sizes for each different adjustable mold.
The same deficiencies resulting from using .DELTA.T for gauging heat removal from the mold apply to the caster spray cooling and roll cooling zones as well.